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  1. #1

    CDI/Coil Interchange on 780SLT

    Guys,

    I have a 1997 SLT780. I believe I might have an electrical/ignition problem. What years/models can I use the CDI and the coils from for replacement?


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Coils from a 650/750/780 from 94 to 97.

    CDI 96 or 97 SLT 780.

    You may be able to use a 94 or 95 750 CDI also. But it won't have the low fuel rev limiter. (750 has 24* of timing, same as the SLT's. HOWEVER, in my book it does say that some SLT 780 did have 28* of timing, so i'd try to find another SLT 780 CDI)


    What's the problem you're having?

  3. #3
    I rebuilt the entire top end, carburetors and fuel system. It ran awesome but was leaking around the base gaskets due to my stupidity (used gasket goo). Tore it down again, replaced base gaskets. Put it back in the water and it ran awesome again with no more leaking around the base gaskets. Ran it for about 3 hours on and off and then it started to bog slightly coming off idle but was otherwise fine. Then it started bogging off idle and missing randomly and not getting up to speed well but would clear up after a few seconds. Then it kept doing the same thing but it would speed up and slow down and speed up and slow down. It acted like it was fuel starved so I rebuilt the pump again but nothing changed. I also did the volume test in the Clymer and the pump checked out OK. So...I can only assume it's electrical in nature???

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    I'm going to guess it's carb/fuel related.

    Did you check for kinks in the lines?

    Did you inspect/replace the petcock?

    Is there water in the fuel seperator?

    When you went through the carbs did you replace the needles and seats? Or at the very least, the N/S O ring?

    May have a bad reed. Does one of the carbs spit alot of gas out the top at idle?

  5. #5
    The lines are brand new, and not kinked. I get fuel out of the return line when the engine is running so I believe enough is reaching carbs. . The petcock is brand new because I broke it getting the old lines off. There is no water in the fuel seperator, checked that first. The needles and seats were not included in the rebuild kit but they looked great. I did replace all the seals and o-rings. I have not seen any gas spitting out any of the carbs at idle. So.......I suppose a reed is a possiblity but how would I check that without pulling it apart? Why don't you think it could be electrical.

    Quote Originally Posted by xlint89 View Post
    I'm going to guess it's carb/fuel related.

    Did you check for kinks in the lines?

    Did you inspect/replace the petcock?

    Is there water in the fuel seperator?

    When you went through the carbs did you replace the needles and seats? Or at the very least, the N/S O ring?

    May have a bad reed. Does one of the carbs spit alot of gas out the top at idle?

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by toddkageals View Post
    Ran it for about 3 hours on and off and then it started to bog slightly coming off idle Then it started bogging off idle and missing randomly and not getting up to speed well but would clear up after a few seconds. Then it kept doing the same thing but it would speed up and slow down and speed up and slow down. It acted like it was fuel starved so I rebuilt the pump again but nothing changed.
    Quote Originally Posted by toddkageals View Post
    The needles and seats were not included in the rebuild kit but they looked great. I did replace all the seals and o-rings. I have not seen any gas spitting out any of the carbs at idle. So.......I suppose a reed is a possiblity but how would I check that without pulling it apart? Why don't you think it could be electrical.
    The reason I don't think it's elec is because your above description doesn't sound electrical. You actually described it as feeling fuel starved yourself.

    If it were elec, normally it will just quit or misfire under load all the time.

    The gradual bog getting worse sounds like a blockage or the fuel "drip" getting worse.

    No way to check reeds without disassembly. If one is damaged, normally you will see alot of fuel spitting from that carb throat.

    Did you replace the fuel filters inside the carbs during rebuild?

    Rebuild kits come with O rings for the needle and seats, did you replace them?

    Did you check the pick up tube for obstructions?

    Run it at idle without the FA on, can you see fuel dripping from any of the carbs?

    Take your plug wrench with you next time out. Warm the engine up like normal, then nail the throttle and make it bog out. Check the spark plugs right then and there. Are they wet or dry?

    Next test, run it WOT until you get the "miss" then pull the lanyard immediately and check the spark plugs then. Wet or dry?

    Have you tried clipping the plug wires back 1/4" yet?

  7. #7
    Well...here's some more information from today. I took off the air cleaner, tied it to the dock and then ran it while looking down the throat of the carburetors. I ran it at about 3/4 throttles and all carbs. seem to be getting plenty of fuel. You can actually see the tiny droplets spraying out of the side of the carbs. I'm not sure what you mean when you say spitting. If you are saying that air is being blown out the top of the carb and is carrying fuel with it, I did not notice any of that. I rode it around for a while. The longer I rode it, the worse it got. It eventually developed a very regular miss. It's also idling rough. I tried pulling off each spark plug wire one at a time while it was idling and nothing really changed whenever I removed a wire. I am fairly certain at this point that it's not fuel related. Reeds...possibly but I still think it's an electrical problem of some type (plug, wires, coils, CDI???). I ran a compression check once I got it back to the house. The engine was cold, throttle wide open, all plugs out. I got 105, 120, 130 MAG to PTO order. I assume this is OK given that I have been through less than 10 gallons since the rebuild and the engine was cold. Anyway, if it's not mechanical, not fuel, that leaves reeds and electrical correct? I'd really hate to throw a CDI at it but I'm not sure what else to do.

  8. #8
    Have not done anything to the wires. What exactly do I need to do?

  9. #9

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    Seems to me that your mag compression is way low.

    For the plug wires you just pull the boots off, cut 1/4" off the wires and screw the boots back on. think there is even a video in the how to section.

    Really doesn't sound like it's electrical, sounds like it's definatly fuel related. take the heads off and take some pictures of the pistons so we can see what the wash looks like.

  10. #10

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    also if it's a reed issue that's fuel. Bad idle is also fuel related. Do you have a fuel filter in the line? If so is it clean? If you dont I have a few spares I could get your way let me know.

    Have you checked the check valves yet from the gas tank? You could be loosing pressure there. Dont think this could be it, but are you sure it's not in low fuel limp mode, that would be the only electrical part I could think of.

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